LM1253A National Semiconductor, LM1253A Datasheet - Page 13

• Manufacturer Part Number: LM1253A
• Description: Monolithic Triple 180 MHz I2C CRT Pre-amp With Integrated Analog On Screen Display (OSD) Generator
• Manufacturer: National Semiconductor

Pin Descriptions
Input/Output Schematics
(Continued)
Pin 20 — Digital Supply 5V supply for the OSD section of
the LM1253A. Pins 19 and 20 should be tied together under
normal operating conditions.
Pin 21 — Analog Supply 5V supply for the video section of
the preamp. A 0.1 µF capacitor should be connected be-
tween pin 21 and pin 22, as close as possible to the
LM1253A.
Pin 22 — Analog Ground Ground for the video section of
the LM1253A. All ground pins of the LM1253A should be
connected together by a ground plane under the LM1253A.
See Figure 31 , which shows a sample layout.
Pin 23, 24, and 25 — Green, Red, and Blue Video Out
These pins output the red, green, and blue video information
in the VideoPlex format. These pins are connected to the
LM2453 using as short of traces as possible. An inductor
should be in series with the trace between the preamp and
CRT driver. The value of this inductor depends on the board
layout. Figures 29, 30 show the external schematic of pins
23, 24, and 25, Figure 21 shows the internal schematic.
Pin 26 — V
Out The voltage that the VideoPlex signal is
DS101265-14
REF
referenced to is output on this pin. A 0.1 µF capacitor should
FIGURE 11. Pin 1 (R
V
)
EXT
REF
be connected between this pin and ground and be located
close to the LM1253A. This pin is connected to the V
pin
REF
of the LM2453. A 0.1 µF capacitor also needs to be con-
nected very close to the LM2453. A 100 µF capacitor should
also be connected to this trace. Figures 29, 30 show the ex-
ternal schematic of pin 26, Figure 22 shows the internal
schematic.
Pin 27 — Analog Ground Ground for the band gap refer-
ence section of the LM1253A. All ground pins of the
LM1253A should be connected together by a ground plane
under the LM1253A. See Figure 31 , which shows a sample
layout.
Pin 28 — Analog Supply 5V supply for the band gap refer-
DS101265-15
ence section of the preamp. A 0.1 µF capacitor should be
FIGURE 12. Pin 2 (V Blank Out)
connected between pin 27 and pin 28, as close as possible
to the LM1253A. See Figure 31 , which shows a sample lay-
out.
DS101265-16
FIGURE 13. Pin 3 (V
Cap)
REF
13
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